The Newfoundland Breeding Colony has been developed as a source of laboratory dogs affected with left ventricular hypertrophy (LVH) due to infracoronary left ventricle outflow tract obstruction and other spontaneously occurring heart defects. More than 100 dogs have been reared, all having some form of hereditary subaortic stenosis (SAS), with one family demonstrating pulmonic valve stenosis and SAS. Cardiac catherization of more than 65 dogs has demonstrated varying peak systolic pressure gradients between left ventricle and aorta from less than 5 to greater than 150 mmHg. Laboratory studies are presently underway to define hemodynamic parameters and tissue morphology resultant of Newfoundland discrete SAS. Numbers of animals are designated for regional myocardial blood flow studies of the hypertrophied ventricle, myocardial preservation during cardiopulmonary bypass procedure, evaluation of corrective surgery techniques including aorta-plasty and apico-aorta prosthetic devices.